Industrial production processes and systems historically have been the subject of refinement and improvement, not only with respect to the development of new and improved products, but also with regard to process efficiency. With the advent of computerized control systems, process system throughput rates have been significantly enhanced and labor intensive procedures have been reduced. Of particular note, industrial procedures which necessarily have involved conditions uncomfortable or hazardous to production personnel, in many instances, have been automated to the extent that operators can remain in safe, environmentally controlled regions of a plant facility while still carrying out production functions. Of course, for certain industries, these desirably safe and reasonably comfortable remote control facilities have not been available due to the economic trade-offs involved or the inability of industrial design investigators to achieve adequate remote process control solutions.
The automation of an industrial process is seen to embrace two principal aspects, to wit, the measure of process parameters and the control thereof. Process measurement generally employs sensing devices, for example, thermal measurement component such as thermocouples or spectral devices, electrical and chemical analyzers and the like, while elements utilized in the control of process function additionally will include tractive electromagnetic mechanisms, switching systems, tracking and similar systems involving any of a broad range of electromechanical and solid-state components.
Where industrial process control and monitoring procedures are carried out in large production complexes from environmentally protected control centers, communication between process control and monitoring components and remote control centers is provided by field wiring. This wiring is compiled at one position or another in the vicinity of the production process into cabling which usually extends over considerable distances toward the central control station. Generally, one control or monitoring position or "point" involving, for instance, a switch or thermocouple, will require one pair of wires which extend to the input/output ports of a computer situated at the control center. Often encountered industrial facilities for which remote monitoring and process control are employed are power generating plants, chemical and metals processing plants and the like where, for example, 1,000 points may be controlled or monitored by wire pairs, thus requiring the extension of 2,000 lines to the central control facility. At that facility, these lines are directed through extensive connector cabinet installations and labyrinths of spreaders to extend finally to desired input/output ports, for example, of a computer control. Such facilities generally are of such a physical extent, that the cabling will be positioned over runs typically ranging from 5,000 meters to 10,000 meters. The cost of such installation for this centralized monitoring and control are quite apparent, power plants often providing capital expenditures of about 20 million dollars for cabling. Of course, the upgrading of processes is continually underway in modern industrial facilities and thus, it becomes necessary that such upgrading also contemplate the necessity of "pulling" cable to achieve the desired upgraded control between the production location and remote control center.
The installation of such numerous and lengthy cable communication links also necessarily involves the hazards of interference from plant activity, such as trucks and similar vehicles cause damage and resultant production difficulties.
While the foregoing elaborate monitoring and process control or industrial communications systems are operative, their long term effectiveness is encumbered both by the operational vagaries of the transducing devices they control or monitor, as well as by the unavoidable exposure of extensive cabling to the environment of the plant through which it extends. In consequence, statistically high numbers of process shut-downs or trip points are reached because of the non-reception of control signals by transducing devices or by the alteration of signal levels and the like which may be generated, for example, from thermocouples and the like. More effective remote operations can be achieved where an assurance that signals are received by transducing elements is provided as well as an assurance on the part of central control that switches are closed and switches as well as field wires are functioning. Further, many industrial facilities cannot cost justify remote monitoring and process control in view of the extensive capital expenditures involved as above discussed. For these industries, some form of process monitoring and control is required which is capable of operating within corrosive and prohibitive environments but yet can remain cost effective.